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opengeospatial / sensorthings

The official web site of the OGC SensorThings API standard specification.
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MQTT notify entity changed #90

Closed mjacoby closed 4 years ago

mjacoby commented 4 years ago

Section 14.2.2 Receive updates of a SensorThings entity with MQTT Subscribe of the standard says

MQTT Control Packet: Subscribe

Topic Pattern: RESOURCE_PATH_TO_AN_ENTITY

Example Topic: Datastreams(1)

Response: When a property of the subscribed entity is updated, the service returns a complete JSON representation of the updated entity. http://docs.opengeospatial.org/is/15-078r6/15-078r6.html#91

What exactly is considered to be a property here? Are those only the "primitive properties" or does this include navigation properties? E.g. if I subscribe to /Datastreams(1) and the Thing that is linked to that Datastream is changed, should this trigger a MQTT notification?

hylkevds commented 4 years ago

Personally I would say that navigation properties are not included. If one is interested in the Thing of Datastream 1, the subscription should be on v1.0/Datastreams(1)/Thing.

The reason is that for v1.0/Datastreams(1) the updated entity is the Datastream, but the complete JSON representation of a Datastream does not give any meaningful information (not even the Id) about the Thing. So sending a Datastream representation to the user when the Thing of the Datastream changes does not tell the user anything.

taniakhalafbeigi commented 4 years ago

I personally agree with Hylke as well.